The Effects Of Viscosity On Disk Wind Formation

Highly collimated jets are widely observed from diverse astrophysical environments. This environment contains active galactic nuclei, X-ray binaries, young stellar objects and gamma-ray burst. It is widely accepted that all these systems have accretion disks.There is no generally accepted theory for the formation and collimation of jets. The most promising universal paradigm of jets formation and collimation relies on open large scale magnetic field which is frozen into the accretion disk. Ionized matter is accelerated by magnetic field near accretion disk to form the disk wind. The wind is collimated to a jet by magnetic collimation.According to conventional disk wind launching theory, there is an effective potential(gravitational plus centrifugal) barrier along magnetic field line, when the angle between large scale magnetic field line and midplane of disk is larger than 60°. Matter requires sufficient thermal energy to overcome the effective potential barrier. When the angle is larger than 65°, the barrier is high enough so that matter is difficult to pass through the barrier for typical coronal temperature. a certain potential difference must be overcome even if the angle is less than 60°, if the magnetic fields are strong to influence the rotation of accretion disk. Furthermore, large scale magnetic fields of disk wind model provide a partial radial support against gravity. The angular velocity of the accretion disk is sub-Keplerian under the field shape. It will be more difficult to launch a wind due to the decrease of centrifugal force. In the case of rotating black hole, the critical angle can become larger than 60°. But this region is close to the minimum stable circular orbit, and width of the region is of order of the radius of the minimum stable circular orbit. In general, the current wind launching theory requires that the large scale magnetic field line inclines enough to make an angle less than 60°with the midplane of disk. except that there is an additional energy or wind source. Recently, observation provides a direct evidence that the wind almost launches vertically from the disk in a wide range. There is contradiction between conventional disk wind launching theory and observation. So, new mechanism is required for explanation of jets formation.In this thesis I investigated the magnetohydrodynamic wind launching theory. There is a viscosity in different magnetic surfaces, because these surfaces have different angular velocities. Viscous force curves the large scale magnetic field line. Curved magnetic field line generate a tension force to balance the viscous force. Because, the Lorentz force is perpendicular to magnetic field, a poloidal Lorentz force of large scale magnetic fields is reduced along large scale magnetic field line. When the direction of viscous force opposite to the rotation of field line, the poloidal Lorentz force provides a support against gravity to lift matter along field line. Beyond this top the centrifugal force exceeds the gravity along field line, so matter is unstable to launch a wind. It is similar to the situation at disk surface with the angle less than 60°.